Resistors are common in semiconductor integrated circuits. Resistors exist, for example, in analog and in mixed mode analog and digital circuits. Resistors also exist in input and output circuits as input and output resistors. In addition, resistors may comprise part of an input protection circuit to provide protection of the circuit against electrostatic discharge (ESD) events. In this case, the resistor is used to both attenuate the ESD voltage and to absorb and diffuse ESD energy. Large voltages in the order of thousands of volts may appear across the two terminals of a resistor used for ESD applications.
In integrated circuits resistors may be formed from a poly-crystalline silicon layer, for example. Resistors in integrated circuits may also be formed in a single-crystalline silicon layer. For example, resistors can be formed in a portion of a single-crystal silicon bulk substrate or in a portion of a single crystal silicon layer in a silicon-on-insulator substrate.
As an example, FIG. 1 shows a resistor 100 formed in a portion of a single crystal silicon substrate 102 and defined by isolation structures 106, e.g., shallow trench isolation (STI) or field oxide structures. The resistor body 104 comprises a conductivity type opposite to the substrate 102 doping type, and the resistor body 104 may be defined by the isolation structures 106. Current 108 flows through the resistor body 104 between two terminals 110 coupled at opposite ends of the resistor body 104. The current 108 experiences resistance in the resistor body 104 that is characteristic of a linear current-voltage relationship. Resistors 100 with a resistor body 104 comprising a single-crystalline semiconductor material characteristically demonstrate higher stability and lower noise than conventional poly-crystalline resistor structures.